Abdominal aortic aneurysms (AAA) represent one of the most common types of aneurysms and result in about 15,000 deaths annually in the United States. An aneurysm is produced when a thinning or weak spot in a vessel wall dilates eventually posing a health risk from its potential to rupture, clot, or dissect. An aneurysm frequently occurs in arteries, but may also form in veins. The etiology of aneurysm formation is not entirely understood, but is thought to be related to congenital thinning of the artery, atherosclerotic vessel degeneration, vessel trauma, infection, smoking, high blood pressure, and other causes leading to vessel degeneration. Left untreated, AAA may lead to gradual vessel expansion, thrombus formation leading to stroke or other vessel blockage, vessel rupture, shock, and eventual death.
AAA are generally localized on long abdominal aortic sections below the renal arteries and oftentimes extend into one or both of the iliac arteries. The aneurysm may begin with a small vessel distension that progressively enlarges at a variable and unpredictable rate. An AAA may enlarge at an average rate of about 0.3-0.5 cm per year. The AAA may continue to enlarge in a silent fashion until a catastrophic event, such as a rupture, occurs. The best predictor of rupture risk is size, wherein rupture is relatively uncommon in AAA less than 5 cm. Once reaching about 8 cm, however, there is about a 75 percent chance of rupture within a year. Besides rupture, another risk of AAA is thrombus dissection. As the vessel enlarges, a thrombus may develop in the aneurysm due to perturbations in blood flow dynamics. Pieces of the clot may eventually loosen and carry away, eventually forming blockages in the legs, lungs, or brain.
AAA are most commonly treated in open surgical procedures, where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of the usually fatal ruptured AAA, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, patients suffering from such aneurysms are often elderly and weakened from cardiovascular and other diseases. This factor reduces the number of patients eligible for surgery. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2 to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Even with successful surgery, recovery takes several weeks and often requires a lengthy hospital stay.
To overcome some of the drawbacks associated with open surgery, a variety of endovascular prosthesis placement techniques have been proposed. Without the need for open abdominal surgery, patient complications and recovery time may be significantly reduced. One endovascular AAA repair technique involves a tubular prosthesis deployed by remote insertion through a femoral artery. The prosthesis may include a synthetic graft sheath body supported by an expandable structure such as a stent. The stent may be self-expanding or balloon-expanding and typically is the means for anchoring the prosthesis to the vessel wall. The stent-graft prosthesis acts as a shunt to carry blood flow from a healthy portion of the aorta, through the aneurysm, and into one or both of the iliac artery branches. The prosthesis excludes any thrombus present in the aneurysm while providing mechanical reinforcement of the weakened vessel reducing the risk of dissection and rupture, respectively.
A number of endovascular AAA stent-graft prosthesis designs are known. For aneurysms proximal to the iliac arteries, many of the designs utilize bifurcated structures. Bifurcated stent-graft prostheses generally have a trunk portion with a relatively large lumen deployed in the aorta, and first and second branch portions with smaller branch lumens deployed within each of the iliac arteries. The deployed trunk and branch portions preferably seal to each other and to the healthy vascular walls beyond the aneurysm to isolate the aneurysm from the bloodstream. Advantageously, the aortic blood flow enters the trunk prosthetic lumen, is separated into the two branch prosthetic lumens, and then flows into each of the iliac arteries in a path that approximates that of a normal, healthy vascular system.
A variety of minimally invasive techniques have been suggested for deployment of these bifurcated prostheses, including in situ assembly of multiple prosthetic modules. The primary stent-graft module may include a trunk, a first branch, and a shortened branch. A secondary stent-graft module may include a second branch for operable attachment to the shortened branch of the primary module. In a number of stent graft designs, the second stent-graft module is operably attached by slipping onto or into the shortened branch thereby providing a length of surface overlap. Frictional forces between the overlapping surfaces usually prevent the second branch from detaching from the primary stent-graft module.
Endovascular deployment and assembly of the multiple prosthetic modules may begin whereby the primary stent-graft module is deployed by catheter through a vessel, such as the femoral artery. The trunk may be positioned and attached to the aorta while the first branch may extend into a single iliac artery. The shortened branch may be oriented toward the contralateral, or alternate, iliac artery. The second branch may then be deployed by catheter through the contralateral iliac to the shortened branch of the primary module. The second branch may be operably attached to the shortened branch thereby completing assembly of the continuous bifurcated prosthetic lumen. Such deployment of the second branch can be very straightforward, and in situ assembly of bifurcated prostheses appears to hold significant promise for many abdominal aortic aneurysm patients.
One shortcoming associated with the multi-module prosthetic stent-graft relates to module separation. The AAA may vary widely in location, size, and the distended shape of the aneurysm itself. Particularly after treatment, the aneurysm and associated vessels may drastically change morphology thereby exerting stress forces on the deployed stent-graft. A significant amount of stress may be exerted on the joint between the shortened branch and second branch. With sufficient change in aneurysm morphology and subsequent stress placed on the joint, the module pieces may separate. The patient may have to undergo another treatment given the problem is detected early. Undetected module separation may lead to continued leakage, aneurysm regrowth, and even the more serious problems associated with AAA. Accordingly, it would be advantageous to prevent separation of the stent-graft modules.
Therefore, it would be desirable to provide a bifurcated endoluminal prosthesis including improved contralateral branch docking that overcomes the aforementioned and other disadvantages.